Active Transport Active Transport Requires Energy Why does active - - PowerPoint PPT Presentation

Active Transport

Active Transport Requires Energy

• Why does active transport require energy?

– Molecules are moving against the concentration gradient (low to high concentrations) OR – Process involves changes in membrane structure

• The hydrolysis of ATP provides the energy to fuel

active transport mechanisms

Passive Versus Active Transport

ATP Hydrolysis

• ATP hydrolysis is the catabolic reaction process

by which chemical energy that has been stored in the high-energy bonds in ATP is released by splitting these bonds

Active Transport – Membrane Pumps

• Carrier proteins are used as pumps to move

substances across the membrane from low to high concentration

Active Transport – Carrier Proteins

• The sodium-potassium pump is an example of a

carrier proteins that moves Na+ ions and K+ ions across the membrane against their gradients

Sodium-Potassium Pump

• Found in many plasma membranes
• Pumps out 3 Na+ ions for every 2 K+ ions taken in

against the concentration gradient

• Uses a tremendous amount of cellular energy

(ATP)

Sodium-Potassium Pump

Why is the sodium-potassium (Na+/K+) pump important?

• Needed for proper muscle contraction and nerve

cell impulse conduction

• Prevents the build up of sodium (Na+) within cells

What would happen if too much sodium collected inside cells?

Active Transport – Bulk Transport

• When molecules are too large to move through

a channel protein or by using a carrier protein, vesicles are used to move the “bulk” material

• Endocytosis (into the cell)

– Phagocytosis (cell “eating”) – Pinocytosis (cell “drinking”)

• Exocytosis (out of the cell)

Endocytosis

• Transports substances into the cell
• Cell membrane pinches around the materials, forms

a vesicle and transports the materials into the cell

Example of Endocytosis: cholesterol uptake by cells

Endocytosis - Pinocytosis

• Small amounts of extracellular fluid (and any

dissolved solutes) are taken into the cell

• Also known as “cell drinking”

Endocytosis - Phagocytosis

• Solid materials are taken into cells
• Also known as “cell eating”

Example of Phagocytosis

• Phagocytes are specialized white blood cells that

engulf and digest bacteria and dead or dying cells

Exocytosis

• Transports bulk materials out of the cell
• Vesicles fuse with the cell membrane and

release the contents outside of the cell

Example of Exocytosis

• An example of exocytosis is when neurons

release neurotransmitters between cells to transmit nerve impulses

Endocytosis and Exocytosis Within the Same Cell

Active Transport Concept Map

• Draw a summary concept map in your notes of

active transport mechanisms

Cellular Transport Review Video